1. Technical Field
This invention relates to a device that controls the air input to the fuel/air circuit of a carburetor for an internal combustion engine.
2. Background
Carburetors are devices that make and control the quantity and ratio of a fuel/fair mixture fed to a spark-ignition internal combustion engine. Carburetors generally have a tube called a throat or barrel that is attached to a manifold that supplies one or more engine cylinders. A single or multi-barrel carburetor can feed several cylinders through a manifold or one carburetor can be provided for each cylinder.
The overall volume of fuel/air mixture is controlled by a throttle located in the throat of the carburetor. This can be a butterfly or slide valve. Within the carburetor adjacent to the throat, are interconnected fuel and air passages. These may be arranged in one or more groupings of passages called circuits that eventually discharge fuel/air mixtures into the throat. For example, an idle circuit may discharge a mixture into the throat between the cylinders and the throttle. When the throttle is substantially closed, this circuit controls the idle speed of the engine. A main circuit may discharge into the throat on the other side of the throttle. When the throttle is open, this circuit controls the engine speed and power.
These circuits have a passage connecting the throat to a fuel reservoir fed from a fuel tank through a metering valve. The passage usually passes through a region, sometimes called an emulsion tube, having small holes that are connected through other passages to ambient air. The connection to ambient air, sometimes called an air bleed, is to produce an emulsion of fuel and air, i.e., to aerate the fuel. Aerated fuel is advantageous because it has a lower viscosity flowing into the carburetor throat and vaporizes more readily on the way to the cylinders.
The amount of aeration depends, in part, on the size of the air bleed passage. Often, there is a small orifice or restriction that limits the air flow. Since air flow will depend on air pressure, temperature, and humidity, the size of the restriction is usually a compromise. Sometimes, these restrictions are replaceable with different sizes to compensate, for example, for high altitude operation.
There have been a number of patents related to controlling the air through an air bleed using devices added to conventional carburetors. Typically, they use a variety of sensors and schemes to optimize engine performance by varying the air flow. Starting in about 1980, passenger autos started to use direct fuel injection instead of conventional carburetors and this changeover was complete by about 1990.
Lacking emission control requirements, motorcycle engines, by and large, still do not use fuel injection. Motorcycle carburetors generally use slide valves and have the two fuel/air circuits discussed above plus a pilot circuit that is most effective between idle and about three eights wide-open throttle. When the air input ports to these three circuits is inside the barrel, they are termed air bleeds. They bleed a very small amount of air from the air going down the barrel. When the air intake ports are outside the barrel, they are termed air jets, but the terminology is often interchanged. Herein, air bleed or air jet refers to whatever air intake port provides air to emulsify the fuel. (Motorcycle carburetors also have their barrels extended by demountable tubes termed velocity stacks.)
Currently, most motorcycle engines are 4 cylinder in-line configurations with a single carburetor dedicated to each cylinder. A few are V-4s, again with a carburetor per cylinder and some are V-2 twins with a single carburetor and a manifold.
Even the one carburetor per cylinder layout comes with a wide variety of design detail. Some have replaceable air bleeds while others have a fixed air bleed tube diameter. Unfortunately, none have easily adjustable air bleeds. This makes it difficult to tune this part of the carburetor for best performance under a variety of conditions. Even if available, having more that one carburetor on an engine makes balancing adjustments extremely difficult.
For a long time, it has been known that controlling the air bleed in a carburetor could improve engine performance. U.S. Pat. No. 4,320,731, issued Mar. 23, 1982 to Braun et al., discloses a free standing air bleed control module for an automobile downdraft-type carburetor. On the particular carburetor illustrated, this module can apparently be installed without any modifications other than affixing an air tube. However, there is no provision for a multi-carburetor setup and it requires an electronic control unit. Although the unit is stated to be of conventional design, it might be impractical for a motorcycle, at least as an add-on to an existing carburetion system.
There are a number of non-electronic after-market kits designed to improve motorcycle engine performance. Carburetor kits are available with different size air bleed orifices or jets, needle valves, venturis and the like. Unfortunately, these are not readily adjustable to optimize performance as much as possible or for changing conditions. Engine performance can also be boosted somewhat with after-market exhaust/muffler systems. Unfortunately, these are relatively expensive. Before this invention, there has been no effective, yet practical and economical device for optimizing carburetor and hence engine performance under varying conditions.
Accordingly, the main objective of the invention is to provide a simple control device for a carburetor with a fuel/air circuit having an air bleed input. The device should be relatively economical, easy to install and manually adjustable. In engines with more than one carburetor, the device should provide substantially equal air flow to all carburetors with a single simultaneous adjustment. In engines with carburetors having more than one fuel/air circuit, the device could provide separate adjustments for each of the selected functionally separate fuel/air circuits, but simultaneous adjustment for all the carburetors. The device is designed for motorcycle engines, but should be useful in race cars and the like having similar setups.
An additional optional objective is to modulate the air flow into the device and to the carburetors by locating the source of air into the device in different air stream environments; quiescent, pointed into an air stream, and away from one. Another optional objective is to provide a remote control.
These objectives are realized by a device having an air distribution block having at least one air input port and a sufficient number of air valves and air output ports for the particular engine. For a single carburetor with a single selected air bleed, one valve and one air output are required. For multiple carburetors, each with one selected air bleed, one valve and a number of air output ports equal to the number of carburetors are required. Substantially equal air flow to multiple carburetors can be enhanced by utilizing a chamber to balance flow to the air outputs and a symmetrical layout for them. For a single carburetor with two selected air bleeds, two valves separately connected to two air outputs are required. Lastly, for an engine with multiple carburetors each having two selected fuel/air circuits with air bleeds, two valves, each separately connected to an air output for each carburetor, are required. Sufficient air tubing is required to connect the air outputs to the carburetor air bleeds.
Optionally, an additional air tube may provided so that the source of air for the air distribution block input or inputs may be located in selected locations, for example, in a carburetor air stream. Another option is to provide a remote control from, for example, the handlebars of a motorcycle.